Determining extended capability of a channel path

ABSTRACT

A computer program product includes a tangible storage storing instructions for performing a method. The method includes receiving a request at a channel subsystem in a host computer system from an operating system in the host computer system to provide a channel path description for a channel path, the channel subsystem configured to direct information flow between memory and the control unit via the channel path; and outputting from the channel subsystem to the operating system, a channel path description block including the channel path description for the channel path in response to the request. The channel path description block includes: a descriptor field (DESC) indicating that the channel path supports a Fibre Channel protocol for commanding an I/O operation; and an extension support indicator field (F) specifying whether the channel path supports an extension to the Fibre Channel protocol.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.12/030,912 filed Feb. 14, 2008, the entire disclosure of which isincorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of Invention

The present disclosure relates generally to input/output processing, andin particular, to determining extended capability of a channel path inan input/output processing system.

2. Description of Background

Input/output (I/O) operations are used to transfer data between memoryand I/O devices of an I/O processing system. Specifically, data iswritten from memory to one or more I/O devices, and data is read fromone or more I/O devices to memory by executing I/O operations.

To facilitate processing of I/O operations, an I/O subsystem of the I/Oprocessing system is employed. The I/O subsystem is coupled to mainmemory and the I/O devices of the I/O processing system and directs theflow of information between memory and the I/O devices. One example ofan I/O subsystem is a channel subsystem. The channel subsystem useschannel paths as communications media. Each channel path includes achannel coupled to a control unit, the control unit being furthercoupled to one or more I/O devices.

The channel subsystem may employ channel command words (CCWs) totransfer data between the I/O devices and memory. A CCW specifies thecommand to be executed. For commands initiating certain I/O operations,the CCW designates the memory area associated with the operation, theaction to be taken whenever a transfer to or from the area is completed,and other options.

During I/O processing, a list of CCWs is fetched from memory by achannel. The channel parses each command from the list of CCWs andforwards a number of the commands, each command in its own entity, to acontrol unit coupled to the channel. The control unit then processes thecommands. The channel tracks the state of each command and controls whenthe next set of commands are to be sent to the control unit forprocessing. The channel ensures that each command is sent to the controlunit in its own entirety. Further, the channel infers certaininformation associated with processing the response from the controlunit for each command.

Performing I/O processing on a per CCW basis may involve a large amountof processing overhead for the channel subsystem, as the channels parseCCWs, track state information, and react to responses from the controlunits. Therefore, it may be beneficial to shift much of the processingburden associated with interpreting and managing CCW and stateinformation from the channel subsystem to the control units. Simplifyingthe role of channels in communicating between the control units and anoperating system in the I/O processing system may increase communicationthroughput as less handshaking is performed. However, altering commandsequences, as well as roles of the channel subsystem and the controlunits, can cause difficulties in interfacing with control units thatsupport different modes of operation in the same I/O processing system.

It would be beneficial to support control units capable of executingcommands absent CCW interpretation by the channels, as well as legacycontrol units that require the channels to parse lists of CCWs. It wouldalso be desirable to support new functionality on a channel path basisas an extension of existing capability, rather than creating an entirelynew channel path type. In order to send commands using such a system, itwould be advantageous to provide notice of the capability supported byeach channel path such that commands can be formatted in compliance witheach channel path configuration. Accordingly, there is a need in the artfor determining extended capability of a channel path in an I/Oprocessing system.

BRIEF SUMMARY OF THE INVENTION

An embodiment of a computer program product for determining extendedcapability of a channel path in an input/output (I/O) processing systemis provided. The computer program product includes a tangible storagemedium readable by a processing circuit and storing instructions forexecution by the processing circuit for performing a method including:receiving a request at a channel subsystem in a host computer systemfrom an operating system in the host computer system to provide achannel path description for a channel path, wherein the channel pathincludes a channel configured to be coupled to a control unit configuredto operate and control one or more I/O devices, the channel subsystemconfigured to direct information flow between memory and the controlunit via the channel path; and outputting from the channel subsystem tothe operating system, a channel path description block including thechannel path description for the channel path in response to therequest. The channel path description block includes: a descriptor field(DESC) indicating that the channel path supports a Fibre Channelprotocol for commanding an I/O operation; and an extension supportindicator field (F) specifying whether the channel path supports anextension to the Fibre Channel protocol.

An embodiment of an apparatus for determining extended capability of achannel path in an input/output (I/O) processing system is provided. Theapparatus includes a channel subsystem in a host computer system forcommunication with a control unit via a channel path, the channelsubsystem including one or more channel paths including one or morechannels configured to be coupled to a control unit configured tooperate and control one or more I/O devices, the channel subsystemconfigured to direct information flow between memory and one or more I/Odevices via the channel path, the channel subsystem configured toperform a method. The method includes: receiving a request at thechannel subsystem from an operating system in the host computer systemto provide a channel path description for the channel path; andoutputting from the channel subsystem to the operating system, a channelpath description block including the channel path description for thechannel path in response to the request. The channel path descriptionblock includes: a descriptor field (DESC) indicating that the channelpath supports a Fibre Channel protocol for commanding an I/O operation;and an extension support indicator field (F) specifying whether thechannel path supports an extension to the Fibre Channel protocol.

A method for determining extended capability of a channel path in aninput/output (I/O) processing system is provided. The method includes:receiving a request at a channel subsystem in a host computer systemfrom an operating system in the host computer system to provide achannel path description for a channel path, wherein the channel pathincludes a channel configured to be coupled to a control unit configuredto operate and control one or more I/O devices, the channel subsystemconfigured to direct information flow between memory and the controlunit via the channel path; and outputting from the channel subsystem tothe operating system a channel path description block including thechannel path description for the channel path in response to therequest. The channel path description block includes: a descriptor fieldindicating that the channel path supports a Fibre Channel protocol forcommanding an I/O operation; and an extension support indicator fieldspecifying whether the channel path supports an extension to the FibreChannel protocol.

Other computer program products, apparatuses, and/or methods accordingto embodiments will be or become apparent to one with skill in the artupon review of the following drawings and detailed description. It isintended that all such additional computer program products,apparatuses, and/or methods be included within this description, bewithin the scope of the present invention, and be protected by theaccompanying claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter which is regarded as the invention is particularlypointed out and distinctly claimed in the claims at the conclusion ofthe specification. The foregoing and other objects, features, andadvantages of the invention are apparent from the following detaileddescription taken in conjunction with the accompanying drawings inwhich:

FIG. 1 depicts one embodiment of an I/O processing system incorporatingand using one or more aspects of the present invention;

FIG. 2A depicts one example of a prior art channel command word;

FIG. 2B depicts one example of a prior art channel command word channelprogram;

FIG. 3 depicts one embodiment of a prior art link protocol used incommunicating between a channel and control unit to execute the channelcommand word channel program of FIG. 2B;

FIG. 4 depicts one embodiment of a transport control word channelprogram, in accordance with an aspect of the present invention;

FIG. 5 depicts one embodiment of a link protocol used to communicatebetween a channel and control unit to execute the transport control wordchannel program of FIG. 4, in accordance with an aspect of the presentinvention;

FIG. 6 depicts one embodiment of a prior art link protocol used tocommunicate between a channel and control unit in order to execute fourread commands of a channel command word channel program;

FIG. 7 depicts one embodiment of a link protocol used to communicatebetween a channel and control unit to process the four read commands ofa transport control word channel program, in accordance with an aspectof the present invention;

FIG. 8 depicts one embodiment of fields in a channel path descriptionblock, in accordance with an aspect of the present invention;

FIG. 9 depicts one embodiment of a channel description specificationdata field in a channel path description block, in accordance with anaspect of the present invention;

FIG. 10 depicts one embodiment of a transport command control block inaccordance with an aspect of the present invention;

FIG. 11 depicts one embodiment of a process for determining extendedcapability of a channel path in an I/O processing system; and

FIG. 12 depicts one embodiment of a computer program productincorporating one or more aspects of the present invention.

The detailed description explains the preferred embodiments of theinvention, together with advantages and features, by way of example withreference to the drawings.

DETAILED DESCRIPTION OF THE INVENTION

In accordance with an aspect of the present invention, input/output(I/O) processing is facilitated. For instance, I/O processing isfacilitated by readily enabling access to information, such as statusand measurement data, associated with I/O processing. Further, I/Oprocessing is facilitated, in one example, by reducing communicationsbetween components of an I/O processing system used to perform the I/Oprocessing. For instance, the number of exchanges and sequences betweenan I/O communications adapter, such as a channel, and a control unit isreduced. This is accomplished by sending a plurality of commands fromthe I/O communications adapter to the control unit as a single entityfor execution by the control unit, and by the control unit sending thedata resulting from the commands, if any, as a single entity.

The plurality of commands are included in a block, referred to herein asa transport command control block (TCCB), an address of which isspecified in a transport control word (TCW). The TCW is sent from anoperating system or other application to the I/O communications adapter,which in turn forwards the TCCB in a command message to the control unitfor processing. The control unit processes each of the commands absent atracking of status relative to those individual commands by the I/Ocommunications adapter. The plurality of commands is also referred to asa channel program, which is parsed and executed on the control unitrather than the I/O communications adapter.

In an exemplary embodiment, the control unit generates a responsemessage in response to executing the channel program. The control unitmay also generate a response message without executing the channelprogram when an exception condition is detected, such as an error in thechannel program that prevents execution. The control unit may include anumber of elements to support communication between the I/Ocommunications adapter and I/O devices, as well as in support of channelprogram execution. For example, the control unit can include controllogic to parse and process messages, in addition to one or more queues,timers, and registers to facilitate communication and status monitoring.The I/O communications adapter parses the response message, extractingthe status and extended status information, and provides feedback toprocessing elements of the I/O processing system.

One example of an I/O processing system incorporating and using one ormore aspects of the present invention is described with reference toFIG. 1. I/O processing system 100 includes a host system 101, whichfurther includes for instance, a main memory 102, one or more centralprocessing units (CPUs) 104, a storage control element 106, and achannel subsystem 108. The host system 101 may be a large scalecomputing system, such as a mainframe or server. The I/O processingsystem 100 also includes one or more control units 110 and one or moreI/O devices 112, each of which is described below.

Main memory 102 stores data and programs, which can be input from I/Odevices 112. For example, the main memory 102 may include one or moreoperating systems (OSs) 103 that are executed by one or more of the CPUs104. For example, one CPU 104 can execute a Linux® operating system 103and a z/OS® operating system 103 as different virtual machine instances.The main memory 102 is directly addressable and provides for high-speedprocessing of data by the CPUs 104 and the channel subsystem 108.

CPU 104 is the controlling center of the I/O processing system 100. Itcontains sequencing and processing facilities for instruction execution,interruption action, timing functions, initial program loading, andother machine-related functions. CPU 104 is coupled to the storagecontrol element 106 via a connection 114, such as a bidirectional orunidirectional bus.

Storage control element 106 is coupled to the main memory 102 via aconnection 116, such as a bus; to CPUs 104 via connection 114; and tochannel subsystem 108 via a connection 118. Storage control element 106controls, for example, queuing and execution of requests made by CPU 104and channel subsystem 108.

In an exemplary embodiment, channel subsystem 108 provides acommunication interface between host system 101 and control units 110.Channel subsystem 108 is coupled to storage control element 106, asdescribed above, and to each of the control units 110 via a connection120, such as a serial link. Connection 120 may be implemented as anoptical link, employing single-mode or multi-mode waveguides in a FibreChannel fabric. Channel subsystem 108 directs the flow of informationbetween I/O devices 112 and main memory 102. It relieves the CPUs 104 ofthe task of communicating directly with the I/O devices 112 and permitsdata processing to proceed concurrently with I/O processing. The channelsubsystem 108 uses one or more channel paths 122 as the communicationlinks in managing the flow of information to or from I/O devices 112. Asa part of the I/O processing, channel subsystem 108 also performs thepath-management functions of testing for channel path availability,selecting an available channel path 122 and initiating execution of theoperation with the I/O devices 112.

Each channel path 122 includes a channel 124 (channels 124 are locatedwithin the channel subsystem 108, in one example, as shown in FIG. 1),one or more control units 110 and one or more connections 120. Inanother example, it is also possible to have one or more dynamicswitches (not depicted) as part of the channel path 122. A dynamicswitch is coupled to a channel 124 and a control unit 110 and providesthe capability of physically interconnecting any two links that areattached to the switch. In another example, it is also possible to havemultiple systems, and therefore multiple channel subsystems (notdepicted) attached to control unit 110.

Also located within channel subsystem 108 are subchannels (not shown).One subchannel is provided for and dedicated to each I/O device 112accessible to a program through the channel subsystem 108. A subchannel(e.g., a data structure, such as a table) provides the logicalappearance of a device to the program. Each subchannel providesinformation concerning the associated I/O device 112 and its attachmentto channel subsystem 108. The subchannel also provides informationconcerning I/O operations and other functions involving the associatedI/O device 112. The subchannel is the means by which channel subsystem108 provides information about associated I/O devices 112 to CPUs 104,which obtain this information by executing I/O instructions.

Channel subsystem 108 is coupled to one or more control units 110. Eachcontrol unit 110 provides logic to operate and control one or more I/Odevices 112 and adapts, through the use of common facilities, thecharacteristics of each I/O device 112 to the link interface provided bythe channel 124. The common facilities provide for the execution of I/Ooperations, indications concerning the status of the I/O device 112 andcontrol unit 110, control of the timing of data transfers over thechannel path 122 and certain levels of I/O device 112 control.

Each control unit 110 is attached via a connection 126 (e.g., a bus) toone or more I/O devices 112. I/O devices 112 receive information orstore information in main memory 102 and/or other memory. Examples ofI/O devices 112 include card readers and punches, magnetic tape units,direct access storage devices, displays, keyboards, printers, pointingdevices, teleprocessing devices, communication controllers and sensorbased equipment, to name a few.

One or more of the above components of the I/O processing system 100 arefurther described in “IBM® z/Architecture Principles of Operation,”Publication No. SA22-7832-05, 6th Edition, April 2007; U.S. Pat. No.5,461,721 entitled “System For Transferring Data Between I/O Devices AndMain Or Expanded Storage Under Dynamic Control Of Independent IndirectAddress Words (IDAWS),” Cormier et al., issued Oct. 24, 1995; and U.S.Pat. No. 5,526,484 entitled “Method And System For Pipelining TheProcessing Of Channel Command Words,” Casper et al., issued Jun. 11,1996, each of which is hereby incorporated herein by reference in itsentirety. IBM is a registered trademark of International BusinessMachines Corporation, Armonk, N.Y., USA. Other names used herein may beregistered trademarks, trademarks or product names of InternationalBusiness Machines Corporation or other companies.

In one embodiment, to transfer data between I/O devices 112 and memory102, channel command words (CCWs) are used. A CCW specifies the commandto be executed, and includes other fields to control processing. Oneexample of a CCW is described with reference to FIG. 2A. A CCW 200includes, for instance, a command code 202 specifying the command to beexecuted (e.g., read, read backward, control, sense and write); aplurality of flags 204 used to control the I/O operation; for commandsthat specify the transfer of data, a count field 206 that specifies thenumber of bytes in the storage area designated by the CCW to betransferred; and a data address 208 that points to a location in mainmemory that includes data, when direct addressing is employed, or to alist (e.g., contiguous list) of modified indirect data address words(MIDAWs) to be processed, when modified indirect data addressing isemployed. Modified indirect addressing is further described in U.S.application Ser. No. 11/464,613, entitled “Flexibly Controlling TheTransfer Of Data Between Input/Output Devices And Memory,” Brice et al.,filed Aug. 15, 2006, which is hereby incorporated herein by reference inits entirety.

One or more CCWs arranged for sequential execution form a channelprogram, also referred to herein as a CCW channel program. The CCWchannel program is set up by, for instance, an operating system, orother software. The software sets up the CCWs and obtains the addressesof memory assigned to the channel program. An example of a CCW channelprogram is described with reference to FIG. 2B. A CCW channel program210 includes, for instance, a define extent CCW 212 that has a pointer214 to a location in memory of define extent data 216 to be used withthe define extent command. In this example, a transfer in channel (TIC)218 follows the define extent command that refers the channel program toanother area in memory (e.g., an application area) that includes one ormore other CCWs, such as a locate record 217 that has a pointer 219 tolocate record data 220, and one or more read CCWs 221. Each read CCW 220has a pointer 222 to a data area 224. The data area includes an addressto directly access the data or a list of data address words (e.g.,MIDAWs or IDAWs) to indirectly access the data. Further, CCW channelprogram 210 includes a predetermined area in the channel subsystemdefined by the device address called the subchannel for status 226resulting from execution of the CCW channel program.

The processing of a CCW channel program is described with reference toFIG. 3, as well as with reference to FIG. 2B. In particular, FIG. 3shows an example of the various exchanges and sequences that occurbetween a channel and a control unit when a CCW channel program isexecuting. The link protocol used for the communications is FICON (FibreConnectivity), in this example. Information regarding FICON is describedin “Fibre Channel Single Byte Command Code Sets-3 Mapping Protocol(FC-SB-3), T11/Project 1357-D/Rev. 1.6, INCITS (March 2003), which ishereby incorporated herein by reference in its entirety.

Referring to FIG. 3, a channel 300 opens an exchange with a control unit302 and sends a define extent command and data associated therewith 304to control unit 302. The command is fetched from define extent CCW 212(FIG. 2B) and the data is obtained from define extent data area 216. Thechannel 300 uses TIC 218 to locate the locate record CCW and the readCCW. It fetches the locate record command 305 (FIG. 3) from the locaterecord CCW 217 (FIG. 2B) and obtains the data from locate record data220. The read command 306 (FIG. 3) is fetched from read CCW 221 (FIG.2B). Each is sent to the control unit 302.

The control unit 302 opens an exchange 308 with the channel 300, inresponse to the open exchange of the channel 300. This can occur beforeor after locate command 305 and/or read command 306. Along with the openexchange, a response (CMR) is forwarded to the channel 300. The CMRprovides an indication to the channel 300 that the control unit 302 isactive and operating.

The control unit 302 sends the requested data 310 to the channel 300.Additionally, the control unit 302 provides the status to the channel300 and closes the exchange 312. In response thereto, the channel 300stores the data, examines the status and closes the exchange 314, whichindicates to the control unit 302 that the status has been received.

The processing of the above CCW channel program to read 4 k of datarequires two exchanges to be opened and closed and seven sequences. Thetotal number of exchanges and sequences between the channel and controlunit is reduced through collapsing multiple commands of the channelprogram into a TCCB. The channel, e.g., channel 124 of FIG. 1, uses aTCW to identify the location of the TCCB, as well as locations foraccessing and storing status and data associated with executing thechannel program. The TCW is interpreted by the channel and is not sentor seen by the control unit.

One example of a channel program to read 4 k of data, as in FIG. 2B, butincludes a TCCB, instead of separate individual CCWs, is described withreference to FIG. 4. As shown, a channel program 400, referred to hereinas a TCW channel program, includes a TCW 402 specifying a location inmemory of a TCCB 404, as well as a location in memory of a data area 406or a TIDAL 410 (i.e., a list of transfer mode indirect data addresswords (TIDAWs), similar to MIDAWs) that points to data area 406, and astatus area 408. TCWs, TCCBs, and status are described in further detailbelow.

The processing of a TCW channel program is described with reference toFIG. 5. The link protocol used for these communications is, forinstance, Fibre Channel Protocol (FCP). In particular, three phases ofthe FCP link protocol are used, allowing host bus adapters to be usedthat support FCP to perform data transfers controlled by CCWs. FCP andits phases are described further in “Information Technology—FibreChannel Protocol for SCSI, Third Version (FCP-3),” T10 Project 1560-D,Revision 4, Sep. 13, 2005, which is hereby incorporated herein byreference in its entirety.

Referring to FIG. 5, a channel 500 opens an exchange with a control unit502 and sends TCCB 504 to the control unit 502. In one example, the TCCB504 and sequence initiative are transferred to the control unit 502 in aFCP command, referred to as FCP_CMND information unit (IU) or atransport command IU. The control unit 502 executes the multiplecommands of the TCCB 504 (e.g., define extent command, locate recordcommand, read command as device control words (DCWs, also referred to asdescriptor control words)) and forwards data 506 to the channel 500 via,for instance, a FCP_Data IU. It also provides status and closes theexchange 508. As one example, final status is sent in a FCP status framethat has a bit active in, for instance, byte 10 or 11 of the payload ofa FCP_RSP IU, also referred to as a transport response IU. The FCP_RSPIU payload may be used to transport FICON ending status along withadditional status information, including parameters that support thecalculation of extended measurement words and notify the channel 500 ofthe maximum number of open exchanges supported by the control unit 502.

In a further example, to write 4 k of customer data, the channel 500uses the FCP link protocol phases, as follows:

1. Transfer a TCCB in the FCP_CMND IU.

2. Transfer the IU of data, and sequence initiative to the control unit502.

(FCP Transfer Ready Disabled)

3. Final status is sent in a FCP status frame that has a bit active in,for instance, byte 10 or 11 of the FCP_RSP IU Payload. The FCP_RSP_INFOfield or sense field is used to transport FICON ending status along withadditional status information, including parameters that support thecalculation of extended measurement words and notify the channel 500 ofthe maximum number of open exchanges supported by the control unit 502.

By executing the TCW channel program of FIG. 4, there is only oneexchange opened and closed (see also FIG. 5), instead of two exchangesfor the CCW channel program of FIG. 2B (see also FIG. 3). Further, forthe TCW channel program, there are three communication sequences (seeFIGS. 4-5), as compared to seven sequences for the CCW channel program(see FIGS. 2B-3).

The number of exchanges and sequences remain the same for a TCW channelprogram, even if additional commands are added to the program. Compare,for example, the communications of the CCW channel program of FIG. 6with the communications of the TCW channel program of FIG. 7. In the CCWchannel program of FIG. 6, each of the commands (e.g., define extentcommand 600, locate record command 601, read command 602, read command604, read command 606, locate record command 607 and read command 608)are sent in separate sequences from channel 610 to control unit 612.Further, each 4 k block of data (e.g., data 614-620) is sent in separatesequences from the control unit 612 to the channel 610. This CCW channelprogram requires two exchanges to be opened and closed (e.g., openexchanges 622, 624 and close exchanges 626, 628), and fourteencommunications sequences. This is compared to the three sequences andone exchange for the TCW channel program of FIG. 7, which accomplishesthe same task as the CCW channel program of FIG. 6.

As depicted in FIG. 7, a channel 700 opens an exchange with a controlunit 702 and sends a TCCB 704 to the control unit 702. The TCCB 704includes the define extent command, the two locate record commands, andthe four read commands in DCWs, as described above. In response toreceiving the TCCB 704, the control unit 702 executes the commands andsends, in a single sequence, the 16 k of data 706 to the channel 700.Additionally, the control unit 702 provides status to the channel 700and closes the exchange 708. Thus, the TCW channel program requires muchless communications to transfer the same amount of data as the CCWchannel program of FIG. 6.

In one embodiment, the I/O processing system 100 of FIG. 1 executes bothCCW channel programs and TCW channel programs on a per channel path 122basis. Thus, while some control units 110 may only support legacy CCWchannel programs, other control units 110 can support extendedcapability of interpreting and performing TCW channel programs. Thechannel subsystem 108 can track the capability of each channel path 122and report the capability to OSs 103 or other programs executed by CPUs104. For example, one of the OSs 103 may send a request to the channelsubsystem 108 for a channel path description to establish the capabilityof channel path 122. The channel subsystem 108 can respond providingcapability information for channel path 122. One example of a responseto a request for a channel path description is depicted in FIG. 8, whichillustrates a channel-path description block 800 in accordance with anexemplary embodiment. As shown in FIG. 8, the channel-path descriptionblock 800 includes a channel path identifier (CHPID) 802, a descriptor(DESC) 804, and channel description specific data (CDSD) 806. It will beunderstood that other fields can be included in the channel-pathdescription block 800 which are not depicted in FIG. 8.

The CHPID 802 may be used to establish the channel path 122 associatedwith the channel-path description block 800. The definition of the CDSD806 can vary based on the value of the DESC 804. For example, when theDESC 804 indicates that channel path 122 of FIG. 1 is capable ofperforming a command mode link protocol (e.g., supporting a FibreChannel link protocol), and an extension to the link protocol isinstalled (e.g., Fibre Channel Extension (FCX) using transport mode),the CDSD 806 may be defined as shown in FIG. 9. In an exemplaryembodiment depicted in FIG. 9, the CDSD 806 includes a max data count902 and an F field 904. The F field 904 is an extension supportindicator that specifies whether the channel path 122 supports anextension to the link protocol, for instance, FCX. The F field 904 mayfurther indicate that the max data count 902 is valid. In an exemplaryembodiment, when the max data count 902 is valid, it contains a 16-bitunsigned integer with a value that is the maximum count of customer datain units of 64K-bytes that the TCCB may transfer. The sum of the databyte count fields in all of the DCWs in a single transport command area(TCA) in a TCCB may not exceed this value. Thus, the count representedby the max data count 902 may be in the range of 65,536 to 4,294,901,760bytes. The relationship of a TCA to a TCCB is further defined inreference to FIG. 10. When the F field 904 indicates that extension tothe link protocol is not supported by the channel path 122, then valuesassociated with the max data count 902 can have an alternate definition,e.g., set to a value of zero. According to an exemplary embodiment, aprogram interface in the host system 101 of FIG. 1, such as OS 103,interprets the amount of customer data that can be sent via the channelsubsystem 108 from a single program-initiated operation when theextension to the link protocol is supported.

FIG. 10 depicts one embodiment of a TCCB 1000 in accordance with anaspect of the present invention. As described previously, the TCCB 1000is a control block built by software and then the channel 124 sends itto a control unit 110 (e.g., in a Transport Command IU) for execution.The TCCB 1000 contains the commands to be executed by the control unit110 and any control data required by the commands. The channel 124 doesnot look at the contents of the TCCB 1000. The channel 124 packages theTCCB 1000 and sends it to the control unit 110. This allows FCPtransport protocols to be utilized instead of FICON, as an extension ofthe command set available for FICON. The TCCB 1000 is part of a TCWchannel program, such as that depicted in FIGS. 4 and 7.

The TCCB 1000 includes a transport control area header (TCAH) 1002which, in an exemplary embodiment, includes information about thetransmit control area (TCA) 1004 and operations within the TCA 1004(e.g., length, service code). In an exemplary embodiment the TCAH 1002includes a format control field for specifying information such as theformat of the TCCB (e.g., variable length CDB format), the modeassociated with the TCCB (e.g., transport mode), service action codesset aside to be used as vendor unique code points, and a field toprovide the control unit the priority in which to execute this TCCB1000.

The TCCB 1000 depicted in FIG. 10 also includes a variable length TCA1004 which includes one or more DCWs 1006 and corresponding DCW controldata 1008, if any for each DCW 1006. As previously described, the maxdata count field 902 of FIG. 9 limits the maximum amount of customerdata that a TCCB may transfer. The DCW control data 1008 may be ofvariable length. In an exemplary embodiment, each DCW 1006 includes acommand code, flags (chaining), control data length (count), andread/write data length (count) fields. The sum of the read/write datalength fields in all of the DCWs in a TCA may not exceed the max datacount field 902. DCW control data 1008 is optional (depending on the DCW1006) and includes control parameters for its corresponding DCW 1006.For example, DCW control data 1008 may include define extent and/orprefix parameters. In an exemplary embodiment, the DCW control data 1008follows its corresponding DCW 1006 within the TCA 1004 and is notpointed to by the DCW 1006. In addition, the TCCB 1000 includes a TCAtrailer (TCAT) 1010 that contains data such as the count of the bytes tobe transferred by the TCCB 1000 and a check word field to check theintegrity of the TCCB 1000.

Turning now to FIG. 11, a process 1100 for determining extendedcapability of a channel path an I/O processing system will now bedescribed in accordance with exemplary embodiments, and in reference tothe I/O processing system 100 of FIG. 1. At block 1102, the channelsubsystem 108 receives a request to provide a channel path descriptionfor channel path 122, where the channel path 122 includes channel 124coupled to control unit 110. OS 103 may initiate the request. In anexemplary embodiment, the link protocol supports CCW channel programsand the extension to the link protocol supports TCW channel programs.For example, the link protocol can be Fibre Channel, and the extensionis FCX.

At block 1104, the channel subsystem 108 outputs the channel pathdescription, for instance, channel-path description block 800 of FIG. 8,for the channel path 122 in response to the request. The channel pathdescription includes a descriptor (DESC 804) indicating that the channelpath 122 supports a link protocol for commanding an I/O operation. Thechannel path description may also include an extension supportindicator, for example, the F field 904 in CDSD 806, specifying whetherthe channel path 122 supports an extension to the link protocol. Thechannel subsystem 108 may output additional information in CDSD 806associated with the descriptor in response to the request, where theCDSD 806 is defined as a function of the descriptor. For example, theCDSD 806 can be a field in the channel-path description block 800 thathas different definitions depending upon the value of the DESC 804. TheCDSD 806 may include the max data count 902 of FIG. 9 indicating amaximum count of customer data the TCCB may transfer, supported by thechannel path 122 when communicating via the extension to the linkprotocol. The CDSD 806 can also include a validity indicatorestablishing validity of the max data count 902. In an exemplaryembodiment, the extension support indicator is the validity indicator,e.g., F field 904 of FIG. 9 provides validity of the max data count 902and indicates that the extension to the link protocol is supported.

Technical effects and benefits of exemplary embodiments includedetermining extended capability of a channel path in an I/O processingsystem. Using one or more fields in a channel path description block todefine channel path capability allows software to determine thecapability of the channel path such that properly formatted CCW or TCWchannel programs can be executed. Advantages include support for bothCCW channel programs and TCW channel programs on a channel path basis inthe same I/O processing system. Further advantages include establishinga configurable maximum amount of customer data that can be transferredto or from the host by a sum of data counts in each DCW in a TCCB of aTCW channel program.

As described above, embodiments can be embodied in the form ofcomputer-implemented processes and apparatuses for practicing thoseprocesses. In exemplary embodiments, the invention is embodied incomputer program code executed by one or more network elements.Embodiments include a computer program product 1200 as depicted in FIG.12 on a computer usable medium 1202 with computer program code logic1204 containing instructions embodied in tangible media as an article ofmanufacture. Exemplary articles of manufacture for computer usablemedium 1202 may include floppy diskettes, CD-ROMs, hard drives,universal serial bus (USB) flash drives, or any other computer-readablestorage medium, wherein, when the computer program code logic 1204 isloaded into and executed by a computer, the computer becomes anapparatus for practicing the invention. Embodiments include computerprogram code logic 1204, for example, whether stored in a storagemedium, loaded into and/or executed by a computer, or transmitted oversome transmission medium, such as over electrical wiring or cabling,through fiber optics, or via electromagnetic radiation, wherein, whenthe computer program code logic 1204 is loaded into and executed by acomputer, the computer becomes an apparatus for practicing theinvention. When implemented on a general-purpose microprocessor, thecomputer program code logic 1204 segments configure the microprocessorto create specific logic circuits.

While the invention has been described with reference to exemplaryembodiments, it will be understood by those skilled in the art thatvarious changes may be made and equivalents may be substituted forelements thereof without departing from the scope of the invention. Inaddition, many modifications may be made to adapt a particular situationor material to the teachings of the invention without departing from theessential scope thereof. Therefore, it is intended that the inventionnot be limited to the particular embodiment disclosed as the best modecontemplated for carrying out this invention, but that the inventionwill include all embodiments falling within the scope of the appendedclaims. Moreover, the use of the terms first, second, etc. do not denoteany order or importance, but rather the terms first, second, etc. areused to distinguish one element from another. Furthermore, the use ofthe terms a, an, etc. do not denote a limitation of quantity, but ratherdenote the presence of at least one of the referenced item.

What is claimed is:
 1. A computer program product for determiningextended capability of a channel path in an input/output (I/O)processing system, the computer program product comprising: a tangiblestorage medium readable by a processing circuit and storing instructionsfor execution by the processing circuit for performing a methodcomprising: receiving a request at a channel subsystem in a hostcomputer system from an operating system in the host computer system toprovide a channel path description for a channel path, wherein thechannel path includes a channel configured to be coupled to a controlunit configured to operate and control one or more I/O devices, thechannel subsystem configured to direct information flow between memoryand the control unit via the channel path; and outputting from thechannel subsystem to the operating system, a channel path descriptionblock including the channel path description for the channel path inresponse to the request, wherein the channel path description blockincludes: a descriptor field (DESC) indicating that the channel pathsupports a Fibre Channel protocol for commanding an I/O operation; andan extension support indicator field (F) specifying whether the channelpath supports an extension to the Fibre Channel protocol.
 2. Thecomputer program product of claim 1, wherein: the extension supportindicator field (F) is contained within a channel description specificdata (CDSD) field.
 3. The computer program product of claim 2, whereinin response to the F field being ‘1’, the CDSD includes a maximum datacount field indicating a maximum count of a sum of data count fields inall device control words (DCWs) in a transport command area (TCA) of acommand message supported by the channel path when communicating via theextension to the Fibre Channel protocol.
 4. The computer program productof claim 1, wherein the Fibre Channel protocol supports channel commandword (CCW) channel programs configured to support at least one CCW thatspecifies a command for performing an I/O operation, and the extensionto the Fibre Channel protocol supports transport control word (TCW)channel programs configured to support at least one transport commandcontrol block (TCCB), the TCCB configured to be sent from the channelsubsystem to the control unit and configured to hold a plurality ofcommands for performing an I/O operation.
 5. The computer programproduct of claim 1, wherein the descriptor field indicates that thechannel path supports the Fibre Channel protocol, and the extensionsupport indicator field is included in a channel description specificdata (CDSD) field that is defined as a function of the descriptor field.6. The computer program product of claim 3, wherein in response to the Ffield being ‘0’, the maximum data count field has a value of ‘0’.
 7. Thecomputer program product of claim 3, wherein the method furthercomprises: in response to the descriptor field (DESC) not indicatingthat the channel path is capable of performing both a command mode linkprotocol supporting the Fibre Channel protocol and an extension to theFibre Channel protocol using transport mode, the channel descriptionspecific data (CDSD) field absent the extension support indicator field(F) specifying whether the channel path supports an extension to theFibre Channel protocol.
 8. The computer program product of claim 3,wherein the TCA is included in a transport command control block (TCCB)sent from a channel to a control unit, the TCA comprising one or moreDCWs, and wherein the maximum data count field represents a number of64K bytes of data.
 9. An apparatus for determining extended capabilityof a channel path in an input/output (I/O) processing system, theapparatus comprising: a channel subsystem in a host computer system forcommunication with a control unit via a channel path, the channelsubsystem including one or more channel paths including one or morechannels configured to be coupled to a control unit configured tooperate and control one or more I/O devices, the channel subsystemconfigured to direct information flow between memory and one or more I/Odevices via the channel path, the channel subsystem configured toperform a method comprising: receiving a request at the channelsubsystem from an operating system in the host computer system toprovide a channel path description for the channel path; and outputtingfrom the channel subsystem to the operating system, a channel pathdescription block including the channel path description for the channelpath in response to the request, wherein the channel path descriptionblock includes: a descriptor field (DESC) indicating that the channelpath supports a Fibre Channel protocol for commanding an I/O operation;and an extension support indicator field (F) specifying whether thechannel path supports an extension to the Fibre Channel protocol. 10.The apparatus of claim 9, wherein: the extension support indicator field(F) is contained within a channel description specific data (CDSD)field.
 11. The apparatus of claim 10, wherein in response to theextension support indicator field (F) being ‘1’, the CDSD includes amaximum data count field indicating a maximum count of a sum of datacount fields in all device control words (DCWs) in a transport commandarea (TCA) of a command message supported by the channel path whencommunicating via the extension to the Fibre Channel protocol.
 12. Theapparatus of claim 9, wherein the Fibre Channel protocol supportschannel command word (CCW) channel programs configured to support atleast one CCW that specifies a command for performing an I/O operation,and the extension to the Fibre Channel protocol supports transportcontrol word (TCW) channel programs configured to support at least onetransport command control block (TCCB), the TCCB configured to be sentfrom the channel subsystem to the control unit and configured to hold aplurality of commands for performing an I/O operation.
 13. The apparatusof claim 9, wherein the descriptor field indicates that the channel pathsupports the Fibre Channel protocol, and the extension support indicatorfield is included in a channel description specific data (CDSD) fieldthat is defined as a function of the descriptor field.
 14. The apparatusof claim 10, wherein in response to the F field being ‘0’, the maximumdata count field has a value of ‘0’.
 15. The apparatus of claim 10,wherein the method further comprises: in response to the descriptorfield (DESC) not indicating that the channel path is capable ofperforming both a command mode link protocol supporting the FibreChannel protocol and an extension to the Fibre Channel protocol usingtransport mode, the channel description specific data (CDSD) fieldabsent the extension support indicator field (F) specifying whether thechannel path supports an extension to the Fibre Channel protocol. 16.The apparatus of claim 10, wherein the TCA is included in a transportcommand control block (TCCB) sent from a channel to a control unit, theTCA comprising one or more DCWs, and wherein the maximum data countfield represents a number of 64K bytes of data.
 17. A method fordetermining extended capability of a channel path in an input/output(I/O) processing system, the method comprising: receiving a request at achannel subsystem in a host computer system from an operating system inthe host computer system to provide a channel path description for achannel path, wherein the channel path includes a channel configured tobe coupled to a control unit configured to operate and control one ormore I/O devices, the channel subsystem configured to direct informationflow between memory and the control unit via the channel path; andoutputting from the channel subsystem to the operating system a channelpath description block including the channel path description for thechannel path in response to the request, wherein the channel pathdescription block includes: a descriptor field indicating that thechannel path supports a Fibre Channel protocol for commanding an I/Ooperation; and an extension support indicator field specifying whetherthe channel path supports an extension to the Fibre Channel protocol.18. The method of claim 17, wherein: the F Field is contained within achannel description specific data (CDSD) field.
 19. The method of claim18 wherein in response to the extension support indicator field (F)being ‘1’, the CDSD includes a maximum data count field indicating amaximum count of a sum of data count fields in all device control words(DCWs) in a transport command area (TCA) of a command message supportedby the channel path when communicating via the extension to the FibreChannel protocol.
 20. The method of claim 17 wherein the Fibre Channelprotocol supports channel command word (CCW) channel programs configuredto support at least one CCW that specifies a command for performing anI/O operation, and the extension to the Fibre Channel protocol supportstransport control word (TCW) channel programs configured to support atleast one transport command control block (TCCB), the TCCB configured tobe sent from the channel subsystem to the control unit and configured tohold a plurality of commands for performing an I/O operation.
 21. Themethod of claim 17, wherein the descriptor field indicates that thechannel path supports the Fibre Channel protocol, and the extensionsupport indicator field is included in a channel description specificdata (CDSD) field that is defined as a function of the descriptor field.22. The method of claim 18, wherein in response to the F field being‘0’, the maximum data count field has a value of ‘0’.
 23. The method ofclaim 18, further comprising: in response to the descriptor field (DESC)not indicating that the channel path is capable of performing both acommand mode link protocol supporting the Fibre Channel protocol and anextension to the Fibre Channel protocol using transport mode, thechannel description specific data (CDSD) field absent the extensionsupport indicator field (F) specifying whether the channel path supportsan extension to the Fibre Channel protocol.
 24. The method of claim 18,wherein the TCA is included in a transport command control block (TCCB)sent from a channel to a control unit, the TCA comprising one or moreDCWs, and wherein the maximum data count field represents a number of64K bytes of data.